1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive composition which is used for the production of a pressure-sensitive adhesive tape, sheet, or label, etc., and in which no or substantially no organic solvent is used.
2. Description of the Prior Art
Hitherto, a method in which a mixture prepared by adding compounding agents such as a tackifier, a softening agent, a plasticizer, a pigment, etc., to a rubber based or acrylic based polymer is dissolved in an organic solvent, the resulting pressure-sensitive solution containing about 30% by weight of solids is coated on a support such as a plastic sheet, metal foil, etc., in a definite thickness, and then the organic solvent used is evaporated off in a subsequent heating drying step, thereby re-forming an adhesive composed of the above mixture on the support in layer form, has been widely employed to produce pressure-sensitive adhesive tapes, etc.
In accordance with this method, two or more times as much organic solvent as solids is required to be used for the purpose of dissolving the solids constituting the adhesive and to form the adhesive layer. The organic solvent used, however, does not play any role in increasing the pressure-sensitive adhesive properties of the adhesive tape. This method, therefore, suffers from the fault that the use of high amounts of organic solvent requires a heat source and apparatus for evaporating the organic solvent, and apparatus for recovering the organic solvent, thereby increasing the cost of a product.